1. Field of the Invention
This invention relates to humidification systems that are used in heating, ventilating and air conditioning (HVAC) systems. Specifically, this invention relates to an improved apparatus for introducing steam into an airstream in such a system.
2. Description of the Prior Art
Air that contains an inadequate amount of humidity can cause problems that range in severity from merely annoying to extremely expensive or even life threatening. Dry air can make people more susceptible to colds, sore throats and other respiratory problems. It can draw moisture out of materials such as carpet, wood, paper, leather, vinyls, plastics and foods. It can also contribute to the generation of static electricity, which can damage electronically sensitive tapes and disks.
Most modern commercial and industrial buildings are equipped with steam humidifiers mounted within the heating and air conditioning systems. Steam from a steam boiler or district steam system is introduced into the ducted airstream and distributed throughout the building.
Humidification steam cannot be allowed to condense into water in a duct system. Damp areas in ducts become breeding grounds for algae and bacteria, many of which are disease-producing to humans, contaminating to industrial processes, and so forth.
To prevent condensation in a duct, the steam must be totally absorbed by the air before the air carries the steam into contact with any internal devices such as dampers, fans, turning vanes etc., within the duct. The more thoroughly the steam is mixed with the air, the shorter the distance it will travel within the duct before becoming absorbed by the air.
Some duct configurations, due to structural limitations imposed by the building design, have very limited open space downstream of the humidifier for absorption of the steam. Closely spaced multiple steam humidifier dispersion tubes can provide the degree of mixing of steam and air that is necessary to satisfy most applications of this type. However, steam humidifier dispersion tubes can present two operational difficulties in a closely spaced arrangement. Present day steam dispersion tubes are usually constructed with a hot outer jacket that contains steam. The purpose of the jacket is to keep the tube hot in order to prevent the humidification steam from condensing as it passes through the tube. However, in closely spaced multiple tube arrangements, jacketed tubes can present more air flow resistance within the ducting system than is considered desirable. Even more importantly, jacketed tubes add unwanted heat to the airstream due to the exposed outer surface of the hot jacket, adding an unwanted additional refrigeration load during periods of cooling. This disadvantage becomes especially pronounced in large modern office buildings, where a cooling load frequently exists continuously, even in winter, as a result of the building insulation and the considerable heat produced by the occupants and equipment. In such buildings, waste heat from the humidification system is always detrimental.
Insulating the exterior surfaces of the hot jacketing can reduce the heat gain, but further aggravates the air flow resistance problem. An automatic valve can be placed in the steam line supplying steam to the tube jackets and cycling it off and on with the humidifier steam valve. However, the stresses created by the cyclical heating and cooling can cause flexing of the tubes and eventual cracking of the jacket welds.
It is clear there has existed a long and unfilled need in the prior art for a steam injection humidification system that is unaffected by condensation problems, and that is capable of introducing humidity into an airstream consistently and effectively, with a minimum of air flow resistance and a minimum of sensible heat transferred to the airstream.